Add Run with Systemd docs (#111)

Co-authored-by: Cyberes <[email protected]>

docs/administration/run-with-systemd.md

@@ -0,0 +1,47 @@
+# Run with Systemd
+
+For non-Docker users, you could run Opengist as a systemd service.
+
+On Unix distributions with systemd, place the Opengist binary like:
+
+```shell
+sudo cp opengist /usr/local/bin
+sudo mkdir -p /var/lib/opengist
+sudo cp config.yml /etc/opengist
+```
+
+Edit the Opengist home directory configuration in `/etc/opengist/config.yml` like:
+```shell
+opengist-home: /var/lib/opengist
+```
+
+Create a new user to run Opengist:
+```shell
+sudo useradd --system opengist
+sudo mkdir -p /var/lib/opengist
+sudo chown -R opengist:opengist /var/lib/opengist
+```
+
+Then create a service file at `/etc/systemd/system/opengist.service`:
+```ini
+[Unit]
+Description=opengist Server
+After=network.target
+
+[Service]
+Type=simple
+User=opengist
+Group=opengist
+ExecStart=opengist --config /etc/opengist/config.yml
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target
+```
+
+Finally, start the service:
+```shell
+systemctl daemon-reload
+systemctl enable --now opengist
+systemctl status opengist
+```